Kaon flow as a probe of the kaon potential in nuclear medium.

The flow of kaons, i.e., the average kaon transverse momentum as a function of rapidity, and the associated flow parameter in heavy-ion collisions at SIS/GSI energies is investigated in the relativistic transport model. It is found that the pattern of kaon flow at the final stage is sensitive to the kaon potential used in the model and is thus a useful probe of the kaon potential in a nuclear medium. Typeset using REVTEX 1 Kaon properties in dense nuclear matter is a subject of considerable current interest. This knowledge is useful for our understanding of both chiral symmetry restoration in dense matter and the properties of the dense nuclear matter existing in neutron stars [1,2] and formed in heavy-ion collisions [3,4]. The possibility of s-wave kaon condensation in dense nuclear matter was first predicted by Kaplan and Nelson [5] based on the mean-field approximation to the chiral Lagrangian. Since then, there have been numerous studies on the properties of kaons in nuclear matter, based on various theoretical approaches such as the effective chiral Lagrangian [6–9], the Nambu−Jona-Lasinio (NJL) model [10], and the phenomenological off-shell meson-nucleon interaction [11]. The predictions from these models, however, have been inconsistent with each other, especially concerning the higher-order corrections beyond the mean-field approximation. In the mean-field approximation to the effective SU(3)L×SU(3)R chiral Lagrangian [5,7], the kaon energy in a nuclear matter satisfies ω(k, ρ) = m2K + k 2 − ΣKN f 2 K ρS + 3 4 ρ f 2 K ω(k, ρ), (1) where mK and k are the kaon mass (in free space) and momentum, respectively. The third term in the above equation is from the attractive scalar interaction due to chiral symmetry breaking and is determined by the kaon-nucleon sigma term ΣKN ≈ 350 MeV, the nuclear scalar density ρS, and the kaon decay constant fK , which is normally assumed to be the same as the pion decay width, i.e., fK ∼ fπ ∼ 93 MeV. The last term is from the repulsive vector interaction and is proportional to the nuclear density ρ. From Eq. (1), we obtain the kaon energy in a nuclear medium